Avoid white spaces or other weird characters on font asset paths.

[matiasbenedetto]

What ?

If you upload a font with spaces in any of the components that end up in the file name of the font asset the resulting font URL has a space and that causes problems.

For example: if you upload a variable font with a font weight of "100 900", the resulting font path in theme.json would be font-name_normal_100 900.ttf and that can be problematic.

With this change, we would have font-name_normal_100-900.ttf.

How to test:

1. Upload a font with variable width. Example: Literata variable (external link because GitHub doesn't allow ttf files).
2. Test that the font asset filename and font path in theme.json don't have white spaces.

[mikachan]

Nice, LGTM 👍